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It has been proved that nanosilica can improve the mechanical properties of cement soil, however, the static and dynamic properties of nanosilica modified cement soil and dispersion method study of nanosilica in cement soil were few, thereby investigated by unconfined compression test and dynamic triaxial test in this study. A series of unconfined compression test results indicated that the dispersion method of nanosilica is of importance in the strength of nanosilica modified cement soil (NCS), and soaking in water for 24 h is the optimal dispersion method among designed methods. Unconfined compressive strength (UCS) increases with increasing nanosilica content in the range of 0 to 0.4%, and then reduces gradually while nanosilica content is beyond 0.4%. The optimal nanosilica content can be seen as 0.4%, and the corresponding UCS at the curing age of 7 d is 960 kPa, which increases by 47.2% comparing to the specimen without nanosilica. Dynamic triaxial test reveals that the variation of the cumulative plastic axial strain and dynamic elastic modulus versus nanosilica content are same and opposite to UCS respectively, and the minimum of the cumulative plastic axial strain and maximum of dynamic elastic modulus are obtained while nanosilica content is 0.4%, which reduces by 48.1% and increases by 69.8% respectively comparing to the specimen without nanosilica. Finally, a simple and practical prediction model is developed to capture the evolution of the cumulative plastic axial strain with cycle number, and its simulation effect is validated by dynamic triaxial test results. It is believed that this paper finds an efficient dispersion method of nanosilica in cement soil, and provides the dynamic properties of nanosilica modified cement soil, which can promote practical application of nanosilica in road engineering. [Display omitted] • Soaking in water for 24 h can efficiently increase the dispersion extent of nanosilica in cement soil. • 0.4% is the optimal content of nanosilica to modify cement soil, which can achieve the best strength improvement. • The proposed model has the satisfactory capability to simulate the cumulative strain behavior under cycle load. [ABSTRACT FROM AUTHOR]